Rotational Shape-Memory Actuators and Associated Devices, Systems, and Methods

ABSTRACT

Rotational shape-memory actuators and associated devices, systems, and methods are disclosed. In some embodiments, a rotational shape-memory actuator includes a first anchor, a second anchor, a spring element extending between the first and second anchors, a first shape memory element extending between the first and second anchors, a second shape memory element extending between the first and second anchors, and a communication line wrapped around the first and second shape memory elements. The first and second shape memory elements are configured to transition between a first configuration in which the first and second shape memory elements are twisted together and a second configuration in which the first and second shape memory elements are less twisted together such that transitions of the first and second shape memory elements between the first and second configurations cause the second anchor to rotate with respect to the first anchor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional patent application that claimspriority to and the benefit of U.S. Provisional Patent Application No.61/546,419, filed Oct. 12, 2011, titled “ROTATIONAL SHAPE MEMORYACTUATORS AND ASSOCIATED DEVICES, SYSTEMS, AND METHODS,” and U.S.Provisional Patent Application No. 61/579,984, filed Dec. 23, 2011,titled “ROTATIONAL SHAPE MEMORY ACTUATORS AND ASSOCIATED DEVICES,SYSTEMS, AND METHODS,” each hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The present disclosure relates to rotational actuators and associateddevices, systems, and methods. In some embodiments, the rotationalactuators are particularly suited for use in intravascular andintracardiac imaging devices, including catheters and guidewires.

BACKGROUND

Heart disease is very serious and often requires emergency operations tosave lives. A main cause of heart disease is the accumulation of plaqueinside the blood vessels, which eventually occludes the blood vessels.Several treatments are available to open up the occluded vessel (e.g.,balloon angioplasty, rotational atherectomy, and intravascular stents).Traditionally, surgeons have relied on X-ray fluoroscopic images thatare planar images showing the external shape of the silhouette of thelumen of blood vessels to guide treatment. Unfortunately, with X-rayfluoroscopic images, there is a great deal of uncertainty about theexact extent and orientation of the stenosis responsible for theocclusion, making it difficult to find the exact location of thestenosis. In addition, though it is known that restenosis can occur atthe same place, it is difficult to check the condition inside thevessels after surgery with X-ray. Intravascular imaging, on the otherhand, can be a valuable tool both during interventional procedures as anaid to navigation and for intra-operative feedback and afterinterventional procedures for post-operative feedback regarding theresults of the procedure.

Ultrasonic transducers have been utilized to visualize the inside of theblood vessels. Current ultrasonic transducer devices are mostly based onone or more stationary ultrasound transducers or rotating a singletransducer in parallel to the blood vessels by means of a rotating shaftthat extends along the length of the device to a motor or other rotarydevice located outside the patient. The ultrasonic transducerarrangements of these devices require a relatively large amount spaceinside the device such that overall of diameter of the device cannot bereduced to desired sizes and/or there is not sufficient room within thedevice to accommodate other desired components. Also, for rotatingultrasound transducer arrangements, the rotating shaft required tofacilitate rotation of the ultrasound transducer causes the distal endof the device to be very stiff, which limits the ability of the deviceto go through tortuous vessels. Also, the high speed rotating shaft alsocontributes to distorted non-uniform images when imaging a tortuous pathin the vasculature, which is commonly referred to as non-uniformrotational distortion (NURD).

Optical coherence tomography (OCT) has also been utilized to visualizethe inside of blood vessels based on differential reflectance, but mostrely on a rotating fiber optic that extends along the length of thedevice. This approach also has problems including, for example,implementing the spinning and scanning motion required without damaginga delicate glass or polycarbonate optical fiber. Also, with the actuatormechanism located outside the patient and tip located inside thepatient, inefficiencies and control issues arise from the torque createdby a long, spinning member. In that regard, remote mechanicalmanipulation and a long spinning element distort the image due to NURD.

Accordingly, there remains a need for improved devices, systems, andmethods for controlling motion of imaging elements within anintravascular imaging device. In that regard, there remains a need forimproved rotational actuators sized and shaped for implementation withinintravascular imaging devices sized for introduction into humanvasculature, including intravascular imaging devices having an outerdiameter of 0.018″ or less.

SUMMARY

Embodiments of the present disclosure are directed to rotationalshape-memory actuators and associated devices, systems, and methods.

In one embodiment, a method of manufacturing an intravascular imagingdevice is provided. The method includes providing a first anchor and asecond anchor; fixedly securing a first shape memory element to thefirst anchor and the second anchor; fixedly securing a second shapememory element to the first anchor and the second anchor; and rotatingthe second anchor relative to the first anchor such that the first andsecond shape memory elements are twisted or braided together. In someinstances, the first and second shape memory elements are configured totransition between a first state and a second state such that when thefirst and second shape memory elements are in the first state the firstand second shape memory elements are twisted together and when the firstand second shape memory elements are in the second state the first andsecond shape memory elements are less twisted than in the first state.In that regard, the first state is a martensite state and the secondstate is an austenite state in some instances. The method furtherincludes fixedly securing a spring to the first anchor and the secondanchor in some embodiments. In that regard, the spring may be fixedlysecured to the second anchor while the first and second shape memoryelements are twisted together. In some embodiments, the length betweenthe first anchor and the second anchor is less than 5 mm and, in someinstances, less than 1 mm after the first and second shape memoryelements and the spring are secured thereto. In some instances, themethod further includes fixedly securing the first anchor to a distalportion of a flexible elongate member sized and shaped for introductioninto human vasculature. In that regard, the flexible elongate member maybe a catheter, a guidewire, or other instrument. An imaging element,such as an ultrasound transducer or a reflector, is coupled to thesecond anchor in some instances. In some instances, the method furtherincludes fixedly securing a third shape memory element to the firstanchor and the second anchor such that rotating the second anchorrelative to the first anchor causes the first, second, and third shapememory elements to be twisted or braided together. In some instances,the method further includes fixedly securing a single shape memoryelement to the first anchor and the second anchor such that rotating thesecond anchor relative to the first anchor causes the single shapememory elements to be twisted.

In another embodiment, a rotational actuator is provided. The rotationalactuator includes a first anchor; a second anchor; a spring elementextending between the first and second anchors; a first shape memoryelement extending between the first and second anchors; and a secondshape memory element extending between the first and second anchors. Thefirst and second shape memory elements are configured to transitionbetween a first state and a second state such that when the first andsecond shape memory elements are in the first state the first and secondshape memory elements are in a first configuration in which the firstand second shape memory elements are twisted together and when the firstand second shape memory elements are in the second state the first andsecond shape memory elements are in a second configuration in which thefirst and second shape memory elements are less twisted together than inthe first configuration. Transitions of the first and second shapememory elements between the first and second states cause the secondanchor to rotate about a longitudinal axis with respect to the firstanchor. In some instances, the first and second shape memory elementsare positioned within a lumen defined by the spring element. In someconfigurations, the spring element is configured to urge the first andsecond shape memory elements towards the first configuration. In someembodiments, the first anchor includes an inner conductive portion, anouter conductive portion, and an insulating portion positioned betweenthe inner and outer conductive portions to conductively isolate theinner and outer conductive portions from one another. In some instances,proximal portions of the first and second shape memory alloy elementsare conductively coupled to the inner conductive portion of the firstanchor. Also, in some instances the spring is conductively coupled tothe outer conductive portion of the first anchor.

In yet another embodiment, an intravascular or intracardiac imagingdevice is provided. The intravascular imaging device includes: anelongate flexible member having a proximal portion and a distal portionand an actuator secured to the distal portion of the elongate flexiblemember. The actuator includes: a first anchor fixedly secured to theelongate flexible member; a second anchor spaced distally along alongitudinal axis of the elongate flexible member from the first anchor;a first shape memory element extending between the first and secondanchors; and a second shape memory element extending between the firstand second anchors. The first and second shape memory elements areconfigured to transition between a first state and a second state suchthat when the first and second shape memory elements are in the firststate the first and second shape memory elements are in a firstconfiguration in which the first and second shape memory elements aretwisted together and when the first and second shape memory elements arein the second state the first and second shape memory elements are in asecond configuration in which the first and second shape memory elementsare less twisted together than in the first configuration. Transitionsof the first and second shape memory elements between the first andsecond states cause the second anchor to rotate about the longitudinalaxis of the elongate flexible member. In some embodiments, an imagingelement is coupled to the second anchor such that the imaging elementrotates about the longitudinal axis of the elongate flexible member withthe second anchor. In that regard, the imaging element is at least oneof an ultrasound transducer and a reflector in some instances.

Additional aspects, features, and advantages of the present disclosurewill become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the present disclosure will be describedwith reference to the accompanying drawings, of which:

FIG. 1 is a diagrammatic perspective view of a portion of anintravascular imaging device according to an embodiment of the presentdisclosure.

FIG. 2 is a diagrammatic side view of a rotational actuator according toan embodiment of the present disclosure in a first orientation.

FIG. 3 is a diagrammatic side view of the rotational actuator of FIG. 2,but illustrating the rotational actuator in a second orientation.

Together, FIGS. 4-8 illustrate a method of assembling the rotationalactuator of FIGS. 2 and 3.

FIG. 4 is a diagrammatic side view illustrating anchors of therotational actuator according to an embodiment of the presentdisclosure.

FIG. 5 is a diagrammatic side view illustrating attachment ofshape-memory elements to the anchors of FIG. 4 according to anembodiment of the present disclosure.

FIG. 6 is diagrammatic side view illustrating the positioning of aspring element relative to anchors and shape-memory elements of FIG. 5and attachment of the spring element to one of the anchors according toan embodiment of the present disclosure.

FIG. 7 is a diagrammatic side view illustrating rotation of one of theanchors relative to the other about a longitudinal axis of therotational actuator according to an embodiment of the presentdisclosure.

FIG. 8 is a diagrammatic side view illustrating attachment of the springelement to the other anchor according to an embodiment of the presentdisclosure.

FIG. 9 is a collection of three diagrammatic, schematic views of ashape-memory rotational actuator arrangement illustrating transitionsbetween different states according to an embodiment of the presentdisclosure.

FIG. 10 is a diagrammatic side view of a rotational actuator accordingto another embodiment of the present disclosure in a first orientation.

FIG. 11 is a diagrammatic cross-sectional side view of a portion of therotational actuator of FIG. 10 according to another embodiment of thepresent disclosure.

FIG. 12 is a diagrammatic cross-sectional side view of a distal portionof an intravascular imaging device according to an embodiment of thepresent disclosure showing a rotational actuator of the device in afirst orientation.

FIG. 13 is a diagrammatic cross-sectional side view of the distalportion of the intravascular imaging device of FIG. 12, but showing therotational actuator of the device in a second orientation.

FIG. 14 is a diagrammatic side view of a rotational actuator with animaging element coupled thereto according to an embodiment of thepresent disclosure in a first orientation.

FIG. 15 is a diagrammatic side view of the rotational actuator of FIG.14, but shown without a bias element to better illustrate an arrangementof communication line(s) extending across the rotational actuator to theimaging element.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It is nevertheless understood that no limitation tothe scope of the disclosure is intended. Any alterations and furthermodifications to the described devices, systems, and methods, and anyfurther application of the principles of the present disclosure arefully contemplated and included within the present disclosure as wouldnormally occur to one skilled in the art to which the disclosurerelates. In particular, it is fully contemplated that the features,components, and/or steps described with respect to one embodiment may becombined with the features, components, and/or steps described withrespect to other embodiments of the present disclosure. For the sake ofbrevity, however, the numerous iterations of these combinations will notbe described separately.

In some aspects, embodiments of the present disclosure relate to imagingdevices for imaging within the lumen of a vessel, including both medicaland non-medical applications. However, some embodiments of the presentdisclosure are particularly suited for use in the context of humanvasculature. Imaging of the intravascular space, particularly theinterior walls of human vasculature can be accomplished by a number ofdifferent techniques. Two of the most common are the use of ultrasoundenergy, commonly known as intravascular ultrasound (IVUS) and opticalcoherence tomography (OCT). Embodiments of each of these techniques relyon the imaging device being repeatedly swept, oscillated, or rotated toobtain data suitable for creating an image of the vessel.

To address the limitations of current devices, new rotational actuatorsfor use in intravascular imaging devices are described below. In thatregard, the rotational actuators of the present disclosure utilize oneor more Shape Memory Alloy (SMA) elements to impart rotational motion toan imaging element coupled to the actuator. In some instances, theactuators provide side-looking imaging by rotating the imaging elementabout a longitudinal axis of a flexible elongate member to which theactuator is coupled. In that regard, the small dimensions of theactuators of the present disclosure allow for the diameter of theflexible elongate member to also be very small. For example, the outsidediameter of the elongate member, such as a guidewire or catheter,containing a rotational actuator and an imaging element as describedherein are between about 0.0007″ (0.0178 mm) and about 0.118″ (3.0 mm),with some particular embodiments have outer diameters of approximately0.014″ (0.3556 mm) and approximately 0.018″ (0.4572 mm)). As such, theflexible elongate members incorporating the actuators and imagingarrangements of the present application are suitable for use in a widevariety of lumens within a human patient besides those that are part orimmediately surround the heart, including atriums, ventricles, veins andarteries of the extremities, renal arteries, blood vessels in and aroundthe brain, and other lumens.

Further, the small dimensions of the actuators of the present disclosureallow room within the flexible elongate member for incorporation of thecomponents of one or more additional interventional devices (e.g., guidewires, pressure sensors, temperature sensors, imaging elements, opticalfibers, ultrasound transducers, reflectors, mirrors, prisms, ablationelements, rf electrodes, conductors, etc.) to be included along with theimaging element. Also, because the rotating actuators of the presentdisclosure do not require a rotating shaft or fiber optic cable toextend proximally along the length of the flexible elongate member, theactuators allow the elongate member to have increased flexibility ifdesired. In addition, the lack of rotating shaft extending along thelength of the flexible elongate member eliminates many of the problemsassociated with NURD.

As used herein, “flexible elongate member” or “elongate flexible member”includes at least any thin, long, flexible structure that can beinserted into the vasculature of a patient. While the illustratedembodiments of the “flexible elongate members” of the present disclosurehave a cylindrical profile with a circular cross-sectional profile thatdefines an outer diameter of the flexible elongate member, in otherinstances all or a portion of the flexible elongate members may haveother geometric cross-sectional profiles (e.g., oval, rectangular,square, elliptical, etc.) or non-geometric cross-sectional profiles.Flexible elongate members include, for example, intravascular cathetersand intravascular guidewires. In that regard, intravascular cathetersmay or may not include a lumen extending along its length for receivingand/or guiding other instruments. If the intravascular catheter includesa lumen, the lumen may be centered or offset with respect to thecross-sectional profile of the device.

The rotating actuator mechanisms of the present disclosure are typicallydisposed within a distal portion of the flexible elongate member. Asused herein, “distal portion” of the flexible elongate member includesany portion of the flexible elongate member from the mid-point to thedistal tip. As flexible elongate members can be solid, some will includea housing portion at the distal portion for receiving the actuators ofthe present disclosure. Such housing portions can be tubular structuresattached to the distal portion of the elongate member. Some flexibleelongate members are tubular and have one or more lumens in which theactuator can be positioned within the distal portion.

“Connected” and variations thereof as used herein includes directconnections, such as being glued or otherwise fastened directly to, on,within, etc. another element, as well as indirect connections where oneor more elements are disposed between the connected elements.

“Secured” and variations thereof as used herein includes methods bywhich an element is directly secured to another element, such as beingglued or otherwise fastened directly to, on, within, etc. anotherelement, as well as indirect techniques of securing two elementstogether where one or more elements are disposed between the securedelements.

Movements that are described as “counter” herein are movements in theopposite direction of an initial movement. For example, if an element isrotated clockwise about a longitudinal axis, then rotation in acounterclockwise direction about the longitudinal axis is a movementthat is “counter” to the clockwise rotation. Similarly, if the elementis moved substantially parallel to the longitudinal axis in a distaldirection, then movement substantially parallel to the longitudinal axisin a proximal direction is “counter” to the distal direction movement.

“Reflector” as used herein encompasses any material which reflects orrefracts a substantial portion of ultrasound or light energy directed atit. In some embodiments of the present disclosure, the reflector is amirror. In other embodiments, the reflector is a prism.

Referring now to FIG. 1, shown therein is a portion of an intravascularimaging device 100 according to an embodiment of the present disclosure.In that regard, the intravascular imaging device 100 includes a flexibleelongate member 102 having a distal tip 104. An imaging arrangement 106is positioned within a distal portion of the flexible elongate member102 proximal of the distal tip 104. In some instances, the imagingarrangement 106 is positioned less than 10 cm, less than 5, or less than3 cm from the distal tip. In some instances, the imaging arrangement 106is positioned within a housing of the flexible elongate member 102. Inthat regard, the housing is a separate component secured to the flexibleelongate member 102 in some instances. In other instances, the housingis integrally formed as a part of the flexible elongate member 102.

The imaging arrangement 106 includes an imaging element 108 that iscoupled to a rotational actuator 110. The rotational actuator 110 isconfigured to rotate the imaging element 108 about the longitudinal axisof the flexible elongate member. In that regard, the rotational actuator110 is configured to rotate the imaging element about the longitudinalaxis between about 5 degrees and about 720 degrees. In some particularembodiments, the rotational actuator 110 is configured to rotate theimaging element about the longitudinal axis about 360 degrees. Imagingelement 108 is representative of a component of an ultrasound, OCT,infrared, thermal, or other imaging modality, which includes suchcomponents as imaging transducers, ultrasound transducers, opticalfibers, reflectors, and/or other imaging components. In some instances,the imaging element 108 is arranged to emit and/or reflect energy (e.g.,ultrasound, light, etc.) in a direction generally perpendicular to thelongitudinal axis of the flexible elongate member. In other instances,the imaging element 108 is arranged to emit and/or reflect energy at anoblique angle between 15 degrees and about 165 degrees, with thepreferred angle for side-looking being between about 80 degrees andabout 110 degrees. Angles contemplated include about 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120,125, 130, 135, 140, 145, 150, 155, 160, and about 165 degrees, or canfall within a range between any two of these values.

Referring now to FIGS. 2 and 3, shown therein are aspects of therotational actuator 110. In that regard, FIG. 2 shows the rotationalactuator 110 in a first, twisted orientation and FIG. 3 shows therotational actuator 110 in a second, untwisted orientation. As shown,the rotational actuator includes an anchor 112 and an anchor 114. A pairof shape-memory elements 116 and 118 extend between and are secured tothe anchors 112 and 114. In FIG. 2, the shape-memory elements 116 and118 are twisted together, while in FIG. 3 the shape-memory elements 116and 118 are untwisted. As discussed in greater detail below, transitionsbetween the twisted and un-twisted (or less twisted) orientations of theshape-memory elements 116 and 118 drive the rotational motion of theactuator 110 and, in turn, the imaging element 108. In that regard, insome embodiments, the anchor 112 is configured to be fixedly secured tothe flexible elongate member 102 while the anchor 114 is able to rotatewith respect to the flexible elongate member 102. Accordingly, with theimaging element 108 secured to the anchor 114, rotation of the anchor114 caused by the shape-memory elements 116 and 118 of the rotationalactuator 110 will also cause rotation of the imaging element 108.

The shape-memory elements 116 and 118 can be fabricated from any knownmaterial with shape memory characteristics. In some embodiments, theshape-memory elements of the present disclosure are formed of nitinol.In some embodiments, the shape-memory elements are a nitinol wire havinga diameter between about 0.010″ (0.254 mm) and about 0.0005″ (0.0127mm). In one particular embodiment, the shape-memory elements are nitinolwires having a diameter of about 0.001″ (0.0254 mm). Shape-memoryelements can be fabricated to take on a predetermined shape whenactivated. Often activation of a shape-memory element consists ofheating the shape-memory element such that it adopts its trained shape.In some embodiments of the present disclosure, this is accomplished byapplying an electric current across the shape-memory elements. In thatregard, in some embodiments two or more conductors extend along thelength flexible elongate member to apply electrical current to theshape-memory elements to facilitate activation of the shape-memoryelements. Activation of the shape-memory elements to cause a deformationto their trained shape can impart a force that can be utilized to causerotational movement. For example, as shown in FIG. 3, the shape-memoryelements 116 and 118 have been trained to have a straightenedorientation in their activated state (e.g., austenite state).Accordingly, by activating (e.g., heating) the shape-memory elements 116and 118, the shape-memory elements 116 and 118 will transition from thetwisted orientation of FIG. 2 to the untwisted or straightenedorientation of FIG. 3. This transition causes rotation of the anchor 114relative to the anchor 112.

Deactivation of a shape-memory element is often achieved by turning offcurrent to the shape-memory element such that the shape-memory elementreturns to its pliable state as it cools. In that regard, the rotationalactuator 110 also includes a bias element 120. The bias element 120 isconfigured to bias the shape-memory elements 116 and 118 towards thetwisted configuration of FIG. 2. In that regard, the bias element 120 iscoupled to the anchors 112 and 114 such that as the anchor 114 rotatesrelative to the anchor 112 upon activation of the shape-memory elements116 and 118, potential energy will be stored in the bias element 120.Accordingly, as the shape-memory elements 116 and 118 cool and return totheir pliable state (e.g., martensite state) the potential energy storedin the bias element 120 will impart a rotational force on theshape-memory elements 116 and 118 that causes them to return to thetwisted orientation of FIG. 2.

Accordingly, by selectively activating and deactivating the shape-memoryelements 116 and 118, repeated rotational movement will be imparted uponanchor 114 relative to anchor 112. In that regard, as the shape-memoryelements 116 and 118 transition from the twisted orientation of FIG. 2to the untwisted orientation of FIG. 3 (as a result of activation of theshape-memory elements), the anchor 114 is rotated in a first direction(e.g., clockwise or counter-clockwise) relative to the anchor 112 aboutthe longitudinal axis 122. Then, as the shape-memory elements 116 and118 transition from the untwisted orientation of FIG. 3 to the twistedorientation of FIG. 2 (as a result of deactivation, or cooling, of theshape-memory elements and the force of bias element 120), the anchor 114is rotated in a second direction that is counter to the first direction(e.g., counter-clockwise or clockwise) relative to the anchor 112 aboutthe longitudinal axis 122. In that regard, the amount of rotationbetween the twisted and untwisted orientations is generally betweenabout 5 degrees and about 720 degrees. However, in other embodiments,the amount of rotation is less than 5 degrees or more than 720 degrees.In some particular embodiments, the amount of rotation between the firstand second orientations of the shape-memory elements 116 and 118 isabout 360 degrees. In some particular embodiments, the shape memoryelements is partially activated via current or heat in order for theshape memory elements to achieve and hold a specific twist level or scanangle. The amount of heat or current passing through the shape-memoryelements balances the heat lost due to passive cooling such that aspecific twist configuration or scan angle is maintained. This can beuseful when a specific scan angle needs to be monitored continuously asa function of time.

While the shape-memory elements are shown as being twisted in FIG. 2 anduntwisted in FIG. 3, this is merely for simple illustration of theunderlying concept. It is understood that in other embodiments theshape-memory elements 116 and 118 transition between two twistedorientations where the first twisted orientation has more twists thanthe second twisted orientation. Further still, in some embodiments theactivated state of the shape-memory elements corresponds to a twistedorientation and the deactivated state corresponds to an untwisted orless twisted orientation.

The bias element 120 provides several important functions in someembodiments. First, as discussed above, the bias element 120 providesthe counterbalance force that re-twists the shape-memory elements 116and 118 as the shape-memory elements passively cool to thelower-temperature martensite state. Second, the bias element keeps theactuator 110 taught between the anchor 112 and the anchor 114,preventing the twisted shape-memory elements 116 and 118 from collapsinginto a ball. In this sense, the bias element provides a structuralintegrity to the actuator 110. In mathematical terms, or topologically,the bias element 120 helps the actuator 110 maintain its twist value andprevents the shape-memory elements from converting the twist to writhe.Finally, the bias element 120 protects the shape-memory elements 116 and118 from physical contact with other parts and liquids. In that regard,the bias element 120 serves as a scaffold or base structure for aninsulating layer (e.g., polyimide tubing) for a further improved levelof electrical and liquid insulation.

In the illustrated embodiment, the bias element 120 is a spring. Thespring material, diameter, pitch, and length are selected to minimizethe size of the actuator while providing the necessary return force andstructural integrity to the actuator. In some instances, the spring isformed of one or more of copper, beryllium copper, aluminum, stainlesssteel, tungsten, brass, or other suitable material. In that regard, theradius (or other cross-sectional measurement for non-circularcross-sectional profiles) of the wire utilized to form the spring isbetween about 0.0003″ (0.00762 mm) and about 0.003″ (0.0762 mm). In someembodiments, the spring has a diameter between about 0.005″ (0.127 mm)and about 0.0393″ (1 mm), a length between about 0.0196″ (0.5 mm) andabout 0.196″ (5 mm), and a pitch between about the thickness of the wireand about 0.0784″ (2 mm). As a general matter, the spring is stifferwhen the spring diameter is decreased, the spring length is decreased,the spring pitch is increased, the radius of the wire used to create thespring is increased, and/or the wire material chosen to create thespring has a higher torsional stiffness.

While the bias element 120 has been illustrated and described as being acoil spring, it is understood that the bias element 120 may be anydevice (or combination of devices) capable of performing the functionsof bias element 120 described above. In some instances, the bias element120 is made from materials that are not rigid, including elastic,superelastic, and non-elastic materials. Suitable materials includetrained and untrained shape-memory alloys including but not limited tonitinol; elastic alloys including but not limited to stainless steel andtitanium alloy; and superelastic alloys including but not limited toCu—Al—Ni, Cu—Al, Cu—Zn—Al, Ti—V, and Ti—Nb alloy.

Referring now to FIGS. 4-8, shown therein are aspects of a method ofassembling the rotational actuator 110 according to one embodiment ofthe present disclosure. As shown in FIG. 4, the anchors 112 and 114 areprovided. In that regard, anchor 112 includes a primary body portion 124and an extension 126. As shown, the primary body portion 124 has adiameter 128. In some instances, the diameter 128 is between about0.005″ (0.127 mm) and about 0.0393″ (1 mm). The extension 126 has adiameter 130 that is less than the diameter 128 of the primary bodyportion 124. In some instances, the diameter 130 is between about 0.002″(0.051 mm) and about 0.0373″ (0.95 mm). Similarly, in some instances thediameter 130 is between about 10% and about 95% of the diameter 128.Generally, the extension 126 serves as an anchor point for the proximalportions of the shape-memory elements extending between the anchors 112and 114. Accordingly, the extension 126 can have any of a variety ofgeometrical profiles, non-geometrical profiles, and/or combinationsthereof. Extension 126 may also have one or more guidance slots, holes,openings, or other structural features that are used for the positioningof the shape memory elements relative to the extension. The structuralfeature(s) may or may not be spaced equally around the circumference ofextension 126. In the case of a single shape memory element actuator, ahole at the center of extension 126 may be used to position shape memoryelement at the center of extension 126.

Similarly, anchor 114 includes a primary body portion 132 and anextension 134. As shown, the primary body portion 132 has a diameter136. In some instances, the diameter 136 is between about 0.005″ (0.127mm) and about 0.0393″ (1 mm). The extension 134 has a diameter 138 thatis less than the diameter 136 of the primary body portion 132. In someinstances, the diameter 138 is between about 0.002″ (0.051 mm) and about0.0373″ (0.95 mm). Similarly, in some instances the diameter 138 isbetween about 10% and about 95% of the diameter 136. Generally, theextension 134 serves as an anchor point for the distal portions of theshape-memory elements extending between the anchors 112 and 114.Accordingly, the extension 134 can have any of a variety of geometricalprofiles, non-geometrical profiles, and/or combinations thereof. In theillustrated embodiment, the anchor 114 is shown as being substantiallyidentical in size and shape as the anchor 112. In other embodiments, theanchors 112 and 114 have one or more different characteristics.Extension 134 may also have one or more guidance slots, holes, openings,or other structural features that are used for the positioning of theshape memory elements relative to the extension. The structuralfeature(s) may or may not be spaced equally around the circumference ofextension 134. In the case of a single shape memory element actuator, ahole at the center of extension 134 may be used to position shape memoryelement at the center of extension 134.

As shown in FIG. 4, the anchors 112 and 114 are positioned such that theextensions 126 and 134 extend towards one another. In some instances,the anchor 112 is configured to be positioned proximal of the anchor 114when attached to the flexible elongate member 102. Accordingly, anchor112 may be considered to be positioned proximal of the anchor 114 suchthat the extension 126 of anchor 112 is positioned distally towardsanchor 114 and the extension 134 of anchor 114 is positioned proximallytowards anchor 112.

Referring now to FIG. 5, the shape-memory element 116 is secured to theextension 126 of anchor 112 by connection 140 and secured to theextension 134 of anchor 114 by connection 142. Similarly, theshape-memory element 118 is secured to the extension 126 of anchor 112by connection 144 and secured to the extension 134 of anchor 114 byconnection 146. In that regard, the connections 140, 142, 144, and 146are representative of any suitable manner of fixedly securing theshape-memory elements 116 and 118 to the anchors 112 and 114. In someinstances, the connections 140, 142, 144, and 146 are one or more of aweld, an adhesive, a mechanical coupling, and/or combinations thereof.As shown, in the illustrated embodiment the shape-memory elements 116and 118 are secured to the anchors 112 and 114 such that they extendrelatively straight across between the anchors. In some embodiments,this straight configuration of the shape-memory elements 116 and 118 isan activated or austenite state (i.e., a trained shape of the material)of the shape-memory elements. In other embodiments, this straightconfiguration of the shape-memory elements 116 and 118 is a deformedmartensite state of the shape-memory elements.

Referring now to FIG. 6, the bias element 120 is positioned over theanchors 112 and 114 and the shape-memory elements 116 and 118. With thebias element 120 positioned over the anchors 112 and 114 and theshape-memory elements 116 and 118, as shown, the bias element 120 issecured to the primary body portion 124 of anchor 112 by connection 148.The connection 148 is representative of any suitable manner of fixedlysecuring the bias element 120 to the anchor 112. In some instances, theconnection 148 is one or more of a weld, an adhesive, a mechanicalcoupling, and/or combinations thereof.

Referring now to FIG. 7, with the bias element secured only to anchor112, anchor 114 is rotated about the longitudinal axis 122 of theactuator as indicated by arrow 150. Generally, the rotation of theanchor 114 can be in either the clockwise or counter-clockwise directionas view along the longitudinal axis 122 from a position distal of theanchor 114. Arrow 150 illustrates a counter-clockwise rotation. Asshown, the rotation of anchor 114 causes the shape-memory elements 116and 118 to twist together. Because the bias element 120 is not connectedto the anchor 114 it is not affected by the rotation of the anchor 114.

Referring now to FIG. 8, while maintaining the anchor 114 in the rotatedposition of FIG. 7 such that the shape-memory elements are twistedtogether, the bias element 120 is secured to the primary body portion132 of anchor 114 by connection 152. The connection 152 isrepresentative of any suitable manner of fixedly securing the biaselement 120 to the anchor 114. In some instances, the connection 152 isone or more of a weld, an adhesive, a mechanical coupling, and/orcombinations thereof. With the bias element 120 secured to anchor 114,the actuator 110 is operationally assembled. In that regard, activationand deactivation of the shape-memory elements 116 and 118 will cause theanchor 114 to rotate about the longitudinal axis of the actuator 110with respect to anchor 112 as discussed above. The assembled actuator110 has outer diameter between about 0.005″ (0.127 mm) and about 0.0393″(1 mm), in some instances. In some particular embodiments, the assembledactuator has an outer diameter of 0.009″, 0.011″, 0.015″, 0.022″,0.028″, or 0.031″. In that regard, in some implementations an actuatorwith an outer diameter of 0.009″ is suitable for use in a 0.011″ guidewire, an 0.011″ outer diameter is suitable for use in a 0.014″ guidewire, an 0.015″ outer diameter is suitable for use in a 0.018″ guidewire, an 0.022″ outer diameter is suitable for use in a 0.025″ guidewire, an 0.028″ outer diameter is suitable for use in a 0.032″ guidewire, an 0.031″ outer diameter is suitable for use in a 0.035″ guidewire, and so on with larger sizes. Generally, the outer diameter of theassembled actuator is less than or equal to the outer diameter of thedevice (e.g., guide wire, catheter, etc.) into which it is incorporated.

With the actuator 110 assembled, the anchor 112 is secured to a flexibleelongate member 102 and an imaging element 108 is secured to anchor 114.As a result, the actuator 110 is able to selectively rotate the imagingelement 108 relative to the flexible elongate member 102 through thetransitions of the shape-memory elements 116 and 118 that cause rotationof the anchor 114. In an alternative embodiment, the anchor 112 iseliminated and the proximal portions of the shape-memory elements 116and 118 are secured directly to the flexible elongate member (or ahousing that is secured to the flexible elongate member). Likewise, insome embodiments, anchor 114 is eliminated and the distal portions ofthe shape-memory elements 116 and 118 are secured directly to theimaging element 108. In other instances, one or more intermediatecomponents are positioned between the proximal and/or distal portions ofthe shape-memory elements 116 and 118 and the flexible elongate member102 and the imaging element 108.

In addition, while FIGS. 2 and 3 show two shape-memory elements (116 and118) in other embodiments a single shape-memory element is used. Using asingle shape-memory allows a further reduction in size of the actuator.In yet other embodiments, three or more shape-memory elements areutilized, including three, four, five, six, seven, eight, nine, and tenshape-memory elements. In that regard, as the number of shape-memoryelements is increased, the resulting rotation of the actuator becomesmore powerful and faster. Accordingly, the number of shape-memoryelements can be selected based on the load of the device or element thatis to be rotated by the actuator in some instances.

Generally, the shape-memory elements are arranged symmetrically as theyextend between the anchors 112 and 114. In some instances, theshape-memory elements are arranged symmetrically about a circumferencesuch that with two shape-memory elements they are spaced apart by 180degrees, with three shape-memory elements they are spaced apart by 120degrees, with four shape-memory elements they are spaced apart by 90degrees, and so on. In other instances, the shape-memory elements arearranged symmetrically, but not about a common circumference. Forexample, with four shape-memory elements, one shape-memory element couldbe centered about a longitudinal axis of the actuator while theremaining three shape-memory elements are equally spaced apart by 120degrees around a circumference spaced from the centered element. In yetother embodiments, the shape-memory elements are arrangednon-symmetrically as they extend between the anchors 112 and 114.

Referring now to FIG. 9, shown therein is a collection 160 of threediagrammatic, schematic views 162, 164, and 166 of a shape-memoryrotational actuator arrangement illustrating transitions betweendifferent states of the shape-memory elements according to aspects ofthe present disclosure. As shown, the actuator includes one or moreshape-memory elements 168 and a structure 170 fixedly coupled to adistal portion of the shape-memory elements 168. A proximal portion ofthe shape-memory elements 168 is fixedly coupled to a structure 172 thatis also configured to selectively apply a current to the shape-memoryelements for selectively activating and deactivating the shape-memoryelements. In that regard, view 162 shows the shape-memory elements 168in a deformed martensite state where the shape-memory elements aretwisted. Arrow 174 represents an application of current to theshape-memory elements 168 that results in a transition of theshape-memory elements 168 to an austenite state (i.e., a trained shapeof the material), as shown in view 164. Though not shown, the untwistingof the shape-memory elements 168 causes twisting of the bias element,which causes potential energy to be stored in the bias element. Arrow176 then represents ceasing application of current to the shape-memoryelements 168 that results in a transition of the shape-memory elements168 to a non-deformed martensite state (i.e., the material is still inthe trained shape, but has become deformable) as shown in view 166.Arrow 178 then represents the application of the potential energy storedin the bias element (created from the untwisting of the shape-memoryelements in the transition associated with arrow 174) being transferredto the shape-memory elements 168, which causes the shape-memory elements168 to twist back to the deformed martensite state of view 162. In someinstances, the transitions associated with arrows 176 and 178 will occurin quick succession or virtually simultaneously. However, the steps havebeen described separately to help facilitate a full understanding of theshape-memory transitions utilized to generate the rotational movement ofthe actuators of the present disclosure.

Referring now to FIGS. 10 and 11, shown therein are aspects of arotational actuator 200 according to another embodiment of the presentdisclosure. The rotational actuator 200 includes many features similarto rotational actuator 110 discussed above. Accordingly, those featureswill not be discussed in detail here, please refer to the descriptionabove. However, the rotational actuator 200 includes a conductivepathway that is particularly suited to facilitate the application ofcurrent to the shape-memory elements of the actuator 200. As shown, therotational actuator 200 includes an anchor 202 and an anchor 204. A pairof shape-memory elements 206 and 208 extend between and are secured tothe anchors 202 and 204. Also, a bias element 210 extends between and issecured to the anchors 202 and 204. As discussed above, transitionsbetween the twisted and un-twisted (or less twisted) orientations of theshape-memory elements 206 and 208 (caused by activating and deactivatingthe shape-memory elements) drive the rotational motion of the actuator200 and, in turn, an imaging element coupled to the actuator. In thatregard, in some embodiments, the anchor 202 is configured to be fixedlysecured to a flexible elongate member while the anchor 204 is able torotate with respect to the flexible elongate member. Accordingly, withthe imaging element secured to the anchor 204, rotation of the anchor204 caused by the shape-memory elements 206 and 208 of the rotationalactuator 200 will also cause rotation of the imaging element.

The shape-memory elements 206 and 208 and the bias element 210 areelectrically coupled to the anchors 202 and 204 in a manner thatfacilitates selective application of current to the shape-memoryelements 206 and 208 to selectively activate and deactivate theshape-memory elements. In that regard, a proximal portion of theshape-memory element 206 is secured to a conductive inner portion 212 ofthe anchor 202 by connection 214. In some instances, the inner portion212 is core wire formed of a conductive material. For example, in oneembodiment the inner portion 212 is a wire having a diameter betweenabout 0.002″ (0.051 mm) and about 0.0373″ (0.95 mm). In one particularembodiment, the inner portion is tungsten wire having 0.004″ diameter. Adistal portion of the shape-memory element 206 is secured to anextension of the anchor 214 by connection 216. Similarly, a proximalportion of the shape-memory element 208 is secured to the inner portion212 of the anchor 202 by connection 218, while a distal portion of theshape-memory element 208 is secured to the extension of the anchor 204by connection 220. Bias element 210, which is formed of a conductivematerial, has a proximal portion that is secured to a conductive outerportion 222 of the anchor 202 by connection 224 and an opposing distalportion that is secured to the anchor 204 by connection 226. A conductor228 is secured to the inner portion 212 of the anchor 202 by connection230, while a conductor 232 is secured to outer portion 222 of the anchor202 by connection 234. In that regard, in some instances outer portion222 of the anchor 202 is a hypotube having an inner diameter betweenabout 0.003″ (0.0762 mm) and about 0.038″ (0.97 mm). Conductors 228 and232 extend proximally along the length a flexible elongate member insome instances. Generally, the connections 214, 216, 218, 220, 224, 226,230, and 234 are representative of an electrical connection. In someinstances, each of the connections 214, 216, 218, 220, 224, 226, 230,and 234 is a weld and/or a mechanical connection. Finally, referring toFIG. 10 and FIG. 11, an insulating layer 236 electrically insulates theinner portion 212 of the anchor 202 from the outer portion 222 of theanchor. In some instances, the insulating layer is formed of polyimide.

As assembled, the actuator 200 provides an electrical path forselectively activating and deactivating the shape-memory elements 206and 208. In that regard, a current supplied along conductor 228 ispassed through inner portion 212 of anchor 202 to the shape-memoryelements 206 and 208. The insulating layer 236 ensures the currenttravels through the shape-memory elements by preventing the current fromshorting through to the outer portion 222 of the anchor 202. From theshape-memory elements 206 and 208, the current passes through the anchor204 to the distal portion of the bias element 210. In that regard,unlike anchor 202 where the inner portion 212 is electrically insulatedfrom the outer portion 222, with anchor 204 the extension and main bodyare electrically coupled such that current received from theshape-memory elements 206 and 208 at the extension passes through theanchor to the distal portion of the bias element. From there, thecurrent travels along the bias element 210 to the outer portion 222 ofthe anchor 202 where conductor 232 is also coupled. In that regard,conductors 228 and 232 are configured to extend proximally through aflexible elongate member where they can be coupled to a voltage sourcefor selective applying the current to the shape-memory elements.

Referring now to FIGS. 12 and 13, shown therein is a distal portion 250of an intravascular imaging device according to another embodiment ofthe present disclosure. FIG. 12 shows a rotational actuator of theintravascular imaging device 200 in a first twisted orientation, whileFIG. 13 shows the rotational actuator in a second untwisted orientation.As shown, the distal portion 250 of the intravascular imaging deviceincludes an outer housing or body 252. An anchor 254 is fixedly securedto the body 252 and an anchor 256 is fixedly secured to the body 252distal of the anchor 254. Between the anchors 254 and 256 is a structure258 that is not secured to the body 252. In that regard, the structure258 is an imaging element in some instances. A plurality of shape-memoryelements 260 extend between and are secured to the anchor 254 and thestructure 258, while at least one bias element extends between and issecured to the structure 258 and the anchor 256. This arrangement of theanchors 254, 256, shape memory elements 260, and bias element 262provides a rotational actuator similar to the rotational actuators 110and 200 discussed above, but where the bias element and the shape-memoryelements are positioned in series, rather than having the shape-memoryelements positioned within the bias element. The resulting functionalityis similar in that transitions between the twisted and un-twisted (orless twisted) orientations of the shape-memory elements 160 drive therotational motion of the structure 258. In that regard, the bias element262 is arranged such that as the structure 258 rotates relative to theanchor 254 upon activation of the shape-memory elements 260 (i.e., thetransition from FIG. 12 to FIG. 13), potential energy will be stored inthe bias element 262. Accordingly, when the shape-memory elements 160are deactivated and return to their pliable state (e.g., martensitestate) the potential energy stored in the bias element 262 imparts acounter rotational force on the shape-memory elements 160 that causesthem to return to the twisted orientation of FIG. 12.

Referring now to FIGS. 14 and 15, shown therein are aspects of arotational actuator 300 according to another embodiment of the presentdisclosure. The rotational actuator 300 includes many features similarto rotational actuators 110 and 200 discussed above. Accordingly, someof the features described with respect to actuator 110 or actuator 200will not be discussed in detail here, please refer to the descriptionabove. An imaging element 301 is coupled to a distal portion of therotational actuator 300. In that regard, to function properly theimaging element 301 requires one or more communication lines to extendto it across the rotational actuator 300. In that regard, imagingelement 301 is representative of a component of an ultrasound, OCT,infrared, thermal, or other imaging modality, which includes suchcomponents as imaging transducers, ultrasound transducers, opticalfibers, optical apertures and/or focusing elements, reflectors, otherimaging components, and/or combinations thereof. Generally, the imagingelement 301 will be an active component of the imaging modality. Thatis, the imaging element 301 will be configured to send and/or receivesignals (e.g., control signals, image data, and/or combinations thereof)over one or more communication pathways to facilitate functioning of theimaging system. In that regard, the limited space within and around therotational actuator 300 to run such communication lines, the stress onthe connections of such communication lines and/or the communicationlines themselves as a result of the rotational movement of the actuator,the electromagnetic interference resulting from the passing of currentthrough the actuator to actuate rotation, interference in the rotationalmovement of the actuator caused by the communication lines, and/or otherfactors impair the ability to simply run the communication lines acrossthe rotational actuator to the imaging element in an suitable andeffective manner. Accordingly, some specific techniques for runningcommunication lines from a proximal portion of the rotational actuator300 to the imaging element 301 at the distal portion of the rotationalactuator are discussed below in the context of exemplary embodiments ofthe present disclosure.

Similar to rotational actuator 200 discussed above, the rotationalactuator 300 includes a conductive pathway that is particularly suitedto facilitate the application of current to the shape-memory elements ofthe actuator 300. As shown, the rotational actuator 300 includes ananchor 302 and an anchor 304. A pair of shape-memory elements 306 and308 extend between and are secured to the anchors 302 and 304. Also, abias element 310 extends between and is secured to the anchors 302 and304. As discussed above, transitions between the twisted and un-twisted(or less twisted) orientations of the shape-memory elements 306 and 308(caused by activating and deactivating the shape-memory elements) drivethe rotational motion of the actuator 300 and, in turn, the imagingelement 301 coupled to the distal portion of the actuator. In thatregard, in some embodiments, the anchor 302 is configured to be fixedlysecured to a flexible elongate member while the anchor 304 is able torotate with respect to the flexible elongate member. Accordingly, withthe imaging element 301 secured to the anchor 304, rotation of theanchor 304 caused by the shape-memory elements 306 and 308 of therotational actuator 300 will also cause rotation of the imaging element301. The imaging element 301 may be secured to the anchor 304 in anysuitable manner including, without limitation, using adhesives (e.g.,epoxy, glue, etc.), mechanical connections, solder, and/or combinationsthereof. In that regard, in some embodiments the imaging element 301 iselectrically isolated from the anchor 304 to prevent the flow of currentthrough anchor 304, as discussed below, from affecting the function ofimaging element 301.

The shape-memory elements 306 and 308 and the bias element 310 areelectrically coupled to the anchors 302 and 304 in a manner thatfacilitates selective application of current to the shape-memoryelements 306 and 308 to selectively activate and deactivate theshape-memory elements. In that regard, a proximal portion of theshape-memory element 306 is secured to a conductive inner portion 312 ofthe anchor 302 by connection 314. In some instances, the inner portion312 is core wire formed of a conductive material. For example, in oneembodiment the inner portion 312 is a wire having a diameter betweenabout 0.002″ (0.051 mm) and about 0.0373″ (0.95 mm). In one particularembodiment, the inner portion is tungsten wire having 0.004″ diameter. Adistal portion of the shape-memory element 306 is secured to anextension of the anchor 314 by connection 316. Similarly, a proximalportion of the shape-memory element 308 is secured to the inner portion312 of the anchor 302 by connection 318, while a distal portion of theshape-memory element 308 is secured to the extension of the anchor 304by connection 320. Bias element 310, which is formed of a conductivematerial, has a proximal portion that is secured to a conductive outerportion 322 of the anchor 302 by connection 324 and an opposing distalportion that is secured to the anchor 304 by connection 326. A conductor328 is secured to the inner portion 312 of the anchor 302 by connection330, while a conductor 332 is secured to outer portion 322 of the anchor302 by connection 334. In that regard, in some instances outer portion322 of the anchor 302 is a hypotube having an inner diameter betweenabout 0.003″ (0.0762 mm) and about 0.038″ (0.97 mm). Conductors 328 and332 extend proximally along the length a flexible elongate member insome instances. Generally, the connections 314, 316, 318, 320, 324, 326,330, and 334 are representative of an electrical connection. In someinstances, each of the connections 314, 316, 318, 320, 324, 326, 330,and 334 is a weld and/or a mechanical connection.

An insulating layer 336 electrically insulates the inner portion 312 ofthe anchor 302 from the outer portion 322 of the anchor. In someinstances, the insulating layer 336 is formed of polyimide. In someinstances, the insulating layer 336 extends distally from the anchor 302to the anchor 304 over the shape-memory elements 306 and 308. Forexample, in some embodiments the insulating layer 336 is formed as asleeve, tube, or similar elongate structure that extends along thelength of the actuator 300 over all or a majority of the length of theshape-memory elements 306 and 308. In other instances, a separateinsulating structure is positioned over the shape-memory elements 306and 308. In some instances, the insulating layer has a thickness betweenabout 0.005″ (0.127 mm) and about 0.01″ (0.254 mm). In one particularembodiment, the insulating layer has a thickness of about 0.005″ (0.127mm). In some instances the insulating layer provides a structure aroundwhich one or more communication lines associated with the imagingelement 301 can be wrapped or coiled in a manner that does not interferewith the rotational function of the actuator 300 and, in particular, theshape-memory elements 306 and 308.

In the illustrated embodiment, a communication line 338 is shownextending from proximal of the anchor 302 distally to the imagingelement 301. A portion 340 of communication line 338 is wrapped orcoiled around the shape-memory elements 306 and 308 and inside of thebias element 310. In that regard, the communication line 338 isrepresentative of any type of communication line or connection that maybe utilized with imaging element 301, including a single electricalconductor or pathway, a plurality of electrical conductors or pathways,a single optical fiber or pathway, a plurality of optical fibers orpathways, and/or combinations thereof. Accordingly, in some instancesthe communication line 338 is configured to extend proximally along amajority of a length of a flexible elongate member. In other instances,the communication line 338 extends to one or more components of animaging arrangement positioned within the flexible elongate memberproximal of the anchor 302. For example, in some instances thecommunication line 338 is coupled to multiplexer(s), opticalconnector(s), and/or other component(s) positioned within a distalportion of the flexible elongate member, but proximal of the anchor 302.

In some embodiments where the communication line 338 includes two ormore communication lines, the plurality of communication lines arecoupled together (e.g., side-by-side, twisted together, wrapped in acommon housing or casing, etc.) such that the plurality of communicationlines form a single structure that is wrapped or coiled around theshape-memory elements 306 and 308. For example, in the illustratedembodiment the communication line 338 consists of two communicationlines 342 and 344 that are coupled to the imaging element 301. However,the communication lines 342 and 344 are coupled together (e.g., as atwisted pair, side-by-side, or other arrangement) along a majority ofthe length of the communication line 338. In that regard, thecommunication lines 342 and 344 are coupled together along the portion340 of the communication line 338 that is wrapped or coiled around theshape-memory elements 306 and 308 (or an insulating layer when aninsulating layer extends over the shape-memory elements 306 and 308). Inother embodiments where the communication line 338 includes two or morecommunication lines, the plurality of communication lines are notcoupled together but instead are each wrapped or coiled separatelyaround the shape-memory elements 306 and 308. In some such instances,the plurality of communication lines are wrapped or coiled separately,but collective form a specific pattern or braiding arrangement.

Wrapping the communication line(s) around the shape-memory elements 306and 308 provides stress relief. In that regard, by wrapping thecommunication line(s) into a spring-like or other flexible form, thecommunication line(s) are able to flex and rotate with the anchor 304 ofthe actuator 300 without undue stress on the communication line(s) orthe connection(s) between the communication line(s) and the imagingelement 301. Further, wrapping the communication line(s) around theshape-memory elements 306 and 308 results in a negligible opposing forceduring the untwisting process and negligible assisting force during thetwisting process. In that regard, compared to the bias element 310 thewrapped communication line(s) provide very little opposing or assistingforce. In that regard, generally speaking, the more times thecommunication line(s) are wrapped around the shape-memory elements 306and 308 the smaller the contribution of the communication line(s) to thetwisting and/or untwisting forces. Accordingly, in some embodiments thecommunication line(s) are wrapped between about 1 and about 100 timesbetween the anchor 302 and the imaging element 301. In that regard, insome instances the communication line(s) are wrapped more than 2 times,more than 3 times, more than 4 times, more than 5 times, more than 10times, more than 20 times, more than 30 times, more than 40 times, morethan 50 times, and/or more than 100 times between the anchor 302 and theimaging element 301.

As assembled, the actuator 300 provides the communication path(s) forcommunicating with the imaging element 301 via communication line 338and also provides an electrical path for selectively activating anddeactivating the shape-memory elements 306 and 308. With respect to theelectrical path, a current supplied along conductor 328 is passedthrough inner portion 312 of anchor 302 to the shape-memory elements 306and 308. The insulating layer 336 ensures the current travels throughthe shape-memory elements by preventing the current from shortingthrough to the outer portion 322 of the anchor 302. From theshape-memory elements 306 and 308, the current passes through the anchor304 to the distal portion of the bias element 310. In that regard,unlike anchor 302 where the inner portion 312 is electrically insulatedfrom the outer portion 322, with anchor 304 the extension and main bodyare electrically coupled such that current received from theshape-memory elements 306 and 308 at the extension passes through theanchor to the distal portion of the bias element 310. However, asdiscussed above, the imaging element 301 is electrically decoupled fromthe anchor 304 in some instances. From anchor 304, the current travelsalong the bias element 310 to the outer portion 322 of the anchor 302where conductor 332 is also coupled. In that regard, conductors 328 and332 are configured to extend proximally through a flexible elongatemember where they can be coupled to a voltage source for selectiveapplying the current to the shape-memory elements.

Persons skilled in the art will also recognize that the apparatus,systems, and methods described above can be modified in various ways.Accordingly, persons of ordinary skill in the art will appreciate thatthe embodiments encompassed by the present disclosure are not limited tothe particular exemplary embodiments described above. In that regard,although illustrative embodiments have been shown and described, a widerange of modification, change, and substitution is contemplated in theforegoing disclosure. It is understood that such variations may be madeto the foregoing without departing from the scope of the presentdisclosure. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the presentdisclosure.

What is claimed is:
 1. A method of manufacturing an intravascular imaging device, comprising: providing a first anchor and a second anchor; fixedly securing a first shape memory element to the first anchor and the second anchor; fixedly securing a second shape memory element to the first anchor and the second anchor; rotating the second anchor relative to the first anchor such that the first and second shape memory elements are twisted together; and wrapping a communication line for an imaging element around the first and second shape memory elements.
 2. The method of claim 1, wherein the first and second shape memory elements are configured to transition between a first state and a second state such that when the first and second shape memory elements are in the first state the first and second shape memory elements are twisted together and when the first and second shape memory elements are in the second state the first and second shape memory elements are less twisted than in the first state.
 3. The method of claim 2, wherein the first state is a martensite state and the second state is an austenite state.
 4. The method of claim 2, further comprising fixedly securing a spring to the first anchor and the second anchor.
 5. The method of claim 4, wherein the spring is positioned around the communication line such that the communication line is positioned between the first and second shape memory elements and the spring.
 6. The method of claim 5, further comprising fixedly securing the first anchor to a distal portion of a flexible elongate member sized and shaped for introduction into human vasculature.
 7. The method of claim 6, wherein an imaging element is coupled to the second anchor.
 8. The method of claim 7, wherein the imaging element is an ultrasound transducer and the communication line comprises an electrical conductor.
 9. The method of claim 7, wherein the imaging element is an optical emitter and the communication line comprises an optical fiber.
 10. The method of claim 6, wherein a length between the first anchor and the second anchor is less than 5 mm after the first and second shape memory elements and the spring are secured thereto.
 11. The method of claim 1, further comprising: fixedly securing a third shape memory element to the first anchor and the second anchor; wherein rotating the second anchor relative to the first anchor causes the first, second, and third shape memory elements to be twisted together.
 12. The method of claim 1, further comprising positioning an insulating member around the first and second shape memory elements, wherein wrapping the communication line for the imaging element around the first and second shape memory elements comprises wrapping the communication line around the insulating member.
 13. The method of claim 1, wherein the communication line comprises a plurality of communication pathways.
 14. The method of claim 13, wherein the plurality of communication pathways is selected from the group of communication pathways consisting of a plurality of electrical pathways, a plurality of optical pathways, and a combination of at least one electrical pathway and at least one optical pathway.
 15. An intravascular imaging device, comprising: a flexible elongate member; a first anchor fixedly secured to the flexible elongate member; a second anchor; an imaging element coupled to the second anchor; a spring element extending between the first and second anchors, a proximal portion of the spring element secured to the first anchor and a distal portion of the spring element secured to the second anchor; a first shape memory element extending between the first and second anchors, a proximal portion of the first shape memory element secured to the first anchor and a distal portion of the first shape memory element secured to the second anchor; a second shape memory element extending between the first and second anchors, a proximal portion of the second shape memory element secured to the first anchor and a distal portion of the second shape memory element secured to the second anchor; and a communication line communicatively coupled to the imaging element, wherein at least a portion of the communication line is wrapped around the first and second shape memory elements; wherein the first and second shape memory elements are configured to transition between a first state and a second state such that when the first and second shape memory elements are in the first state the first and second shape memory elements are in a first configuration in which the first and second shape memory elements are twisted together and when the first and second shape memory elements are in the second state the first and second shape memory elements are in a second configuration in which the first and second shape memory elements are less twisted together than in the first configuration; and wherein the transitions of the first and second shape memory elements between the first and second states cause the second anchor to rotate about a longitudinal axis of the flexible elongate member with respect to the first anchor.
 16. The rotational actuator of claim 15, wherein the first and second shape memory elements are positioned within a lumen defined by the spring element.
 17. The rotational actuator of claim 15, wherein the communication line is positioned between the spring element and the first and second shape memory elements.
 18. The rotational actuator of claim 15, wherein the first anchor comprises: an inner conductive portion; an outer conductive portion; and an insulating portion positioned between the inner and outer conductive portions to conductively isolate the inner and outer conductive portions from one another.
 19. The rotational actuator of claim 18, wherein the proximal portions of the first and second shape memory elements are conductively coupled to the inner conductive portion of the first anchor.
 20. The rotational actuator of claim 19, wherein the spring is conductively coupled to the outer conductive portion of the first anchor.
 21. The rotational actuator of claim 18, wherein the insulating portion extends over the first and second shape memory elements.
 22. The rotational actuator of claim 21, wherein the at least a portion of the communication line is wrapped around the insulating portion.
 23. The rotational actuator of claim 15, further comprising an insulating member positioned around the first and second shape memory elements, wherein the at least a portion of the communication line is wrapped around the insulating member.
 24. The intravascular imaging device of claim 15, wherein the imaging element is an ultrasound imaging element.
 25. The intravascular imaging device of claim 24, wherein the ultrasound imaging element is an ultrasound transducer.
 26. The intravascular imaging device of claim 24, wherein the communication line is at least one electrical conductor.
 27. The intravascular imaging device of claim 15, wherein the imaging element is an OCT imaging element.
 28. The intravascular imaging device of claim 27, wherein the OCT imaging element is at least one fiber optic cable.
 29. A method of manufacturing an intravascular imaging device, comprising: providing a first anchor and a second anchor; coupling an imaging element to the second anchor; fixedly securing a first shape memory element to the first anchor and the second anchor; fixedly securing a second shape memory element to the first anchor and the second anchor; rotating the second anchor relative to the first anchor such that the first and second shape memory elements are twisted together; and fixedly securing a spring to the first anchor and the second anchor; wherein the first and second shape memory elements are configured to transition between a first state and a second state such that when the first and second shape memory elements are in the first state the first and second shape memory elements are twisted together and when the first and second shape memory elements are in the second state the first and second shape memory elements are less twisted than in the first state.
 30. A rotational actuator, comprising: a first anchor; a second anchor; at least one shape memory element extending between the first and second anchors, a proximal portion of the at least one shape memory element secured to the first anchor and a distal portion of the at least one shape memory element secured to the second anchor wherein the at least one shape memory element is configured to transition between a first state and a second state such that when the at least one shape memory element is in the first state the at least one shape memory element is in a first configuration in which the at least one shape memory element is twisted and when the at least one shape memory element is in the second state the at least one shape memory element is in a second configuration in which the at least one shape memory element is less twisted than in the first configuration; and wherein the transitions of the at least one shape memory element between the first and second states cause the second anchor to rotate about a longitudinal axis with respect to the first anchor. 